Flu season is making its miserable presence felt across the United States, with a sharp jump in cases last week propelled by a comeback of the nasty swine flu virus that wreaked havoc in 2009, federal authorities reported.

The number of states reporting “widespread” seasonal flu activity — meaning cases are found in more than half of a state’s counties — spiked from four to ten last week, the Centers for Disease Control and Prevention said in its weekly flu update.

The northeast and mid-Atlantic are especially flu-prone this winter, with New York, Pennsylvania, Virginia and Massachusetts among the ten. The CDC also placed Alaska, Wyoming and Kansas as well as three southern states — Texas, Alabama and Louisiana — on widespread flu alert for the week ending December 21.

Only four states — Alabama, Louisiana, New York and Texas — made the list the week before.

“It’s a typical influenza season, if I can use that word,” said Dr. Michael Jhung, a medical officer in the CDC’s flu division, told CNN. But the resurgence of H1N1, the virus that was dubbed “swine flu,” is a surprise, authorities said.

Flu has killed four children in the U.S. since September 29, according to the CDC, which urges vaccinations to combat the spread of the virus during a flu season that’s expected to last into February.